Electronic devices such as tablet computers, smart phones, smart watches and others often incorporate a touch panel to display information and to receive one or more user inputs made by touching the display. The touch panel is typically a mutual capacitance touch panel with a capacitive sensing medium incorporating a plurality of row electrodes (referred to as transmit electrodes) and a plurality of column electrodes (referred to as receive electrodes) arranged in a rectangular grid pattern. A drive signal voltage is applied on the transmit electrodes and a voltage is measured at each receive electrode. Since the human body is an electrical conductor, when a finger touches or comes close to the touch panel, an electrostatic field of the touch panel is distorted and this produces a measurable change at the receive electrodes.
Coordinates of the user input at the touch panel are computed from the measured change and interpolation may be used to compute coordinates of user input positions within individual cells of the grid rather than at intersections of the grid.
Where a stylus or pen is used in conjunction with the touch panel, the stylus or pen incorporates drive electrodes so that drive electrodes at the touch panel itself may be used as receive electrodes.
Impulse noise can negatively affect the functioning of such touch panels. Impulse noise occurs when energy of a relatively high intensity and short duration flows into the sensor panel, such as from electrostatic charge flowing from a user's body, or from nearby electronic equipment.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known touch panels.